Conventionally, as a both-side grinding method for grinding the surface and back sides of such thin disc work (hereinafter called work), the one disclosed in Japanese Laid-open Patent H11-198009 is available.
In this grounding method, the work is disposed between a pair of cup type grinding wheels rotating at a high speed so that the outer periphery of the work intersects the outer periphery of the grinding surface of the grinding wheel and the center of the work is positioned within the annular grinding surface of the grinding wheel, and the work portion protruded radially outwardly from the outer periphery of the grinding surface is rotationally supported and also the pair of grinding wheels rotating at a high speed are fed in the axial direction of the grinding wheel spindle, then the surface and back sides of the work are held and simultaneously ground by the annular grinding surfaces of both grinding wheels.
And, a distance sensor is moved in the diametric direction of the work after grinding in order to measure the thickness of the work, and the parallelism of the work is enhanced by adjusting the tilt of the grinding wheel in accordance with the result of measurement.
Such a method is intended to obtain a work being high in parallelism of the machined surface by obtaining a work that is constant in thickness.
As the pair of grinding wheels repeat grinding operation, the grinding surface of each grinding wheel wears with the lapse of time, and there arises a difference in the amount of wear between the grinding surfaces of both grinding wheels. As a result, the positions of these grinding surfaces gradually become deviated from the predetermined initial or desired positions.
And, as in the conventional grinding method mentioned above, when the work portion protruded radially outwardly from between the pair of grinding wheels is rotationally supported and the work portion not supported is held and ground by both grinding wheels, if the grinding surface position is deviated from the desired position during grinding, then one of the grinding wheels will touch the work earlier, causing the work to be ground in a bent state. As a result, the work after grinding will be bent and there may arise a problem of its lowering in flatness and the like.
Also, even in case of defective tilt of the grinding wheel spindle due to secular change of component parts of the machine or external factors such as thermal displacement, the work will bend during grinding operation, and there arises a problem the same as mentioned above.
However, in the above grinding method, it is unable to detect the defective tilt of the grinding wheel spindle, and therefore, the problem of bending of the work result therefrom cannot be solved.
The present invention is intended to solve such a conventional problem, and the object of the invention is to provide a both-side grinding method in which the deviation of the grinding wheel caused by wear of the grinding surface of the grinding wheel or defective tilt of the grinding wheel spindle is detected from the amount of work deformation after grinding, and the position of the grinding wheel is correctly adjusted (to correct axial position and tilt), and thereby, work being free from bending and excellent in parallelism and flatness can be obtained.
Also, another object of the present invention is to provide a both-side grinding machine having a configuration that enables the execution of the both-side grinding method.